Lumbar spinal stenosis is a condition of polyetiologic origin. It is defined as narrowing of the spinal canal, the nerve root canals or the intervertebral canals. For clinical, diagnostic and therapeutic reasons it may be divided into two main types: central and lateral stenosis with obstruction of the lateral recesses. Plain radiographs may be suggestive in central or generalized narrowing only. Diagnosis is confirmed by additional investigations, i.e. myelography and CT. Lumbar myelography allows definitive diagnosis of central spinal stenosis. However, validity regarding visualization of the lateral recesses is limited and a decision on the nature of the obstruction, bony or soft tissue, cannot be made. In contrast, CT does support information on the bony outline of the lateral recess as related to the facet and soft tissue structures in particular. Treatment of choice should be conservative-supportive if clinical symptoms permit. Surgery is indicated when there is intolerable pain, progressive muscle weakness or sphincter dysfunction. Surgery seeks to attain complete decompression of neural elements, if instability is present or imminent spinal fusion has to be considered. Shape, size and configuration of the spinal canal have to be determined prior to any surgical approach. CT fulfills these requirements most admirably.